Simplify the following expression: $k = \dfrac{x^2 + 3x - 18}{x + 6} $
Solution: First factor the polynomial in the numerator. $ x^2 + 3x - 18 = (x + 6)(x - 3) $ So we can rewrite the expression as: $k = \dfrac{(x + 6)(x - 3)}{x + 6} $ We can divide the numerator and denominator by $(x + 6)$ on condition that $x \neq -6$ Therefore $k = x - 3; x \neq -6$